Random part of the day: Train Wheel, Dia. 16.6/23 Mm
Posted by Huwbot,
Today's random part is 38340, 'Train Wheel, Dia. 16.6/23 Mm', which is a System part, category Transportation Means, Trains.
Our members collectively own a total of 193,992 of them. If you'd like to buy some you should find them for sale at BrickLink.
36 likes
10 comments on this article
Works great if your minifig wants to do the “spinning plates” trick.
Does anybody know why the old wheels needed a metal axle in the first place?
Huh, I have 20 of these babies; picked up a used Disney Train a couple of weeks ago for less than original retail. One of those sets I didn’t think I’d ever get because of the market value!
The Great Usurper; Harbinger of Doom to metal axles, and Demon of the the new train bogies:
The Plastic Train Axle cometh!
@Norikins:
Short answer: because that’s how they were designed.
Long answer: both versions have advantages and disadvantages. The metal axle reduces friction on the train car, both by keeping the wheels rigidly parallel, and because polished metal contact points create less friction with plastic. The Technic pins create less friction on the tracks because the wheels can rotate independently at different speeds when cornering. But getting back to the short answer, the design was probably borrowed in from traditional hobby trains.
If you really want them to roll smoothly, a lot of people have modded their bogeys to use metal axles combined with sealed ball bearings, combined with slipping rare earth disc magnets between the couplings to strengthen their holding power. I’ve seen club members run trains that are longer than the layout this way, and if you know anything about train physics, pulling rolling stock around two corners simultaneously creates a tremendous amount of drag on the inside rail.
^ Lego and physics. This is a great site.
Metal axles allow more compact, easier to assemble bogies for the 6+ City age group especially when there are a dozen to do. Probably also just a carry over from when vintage trains had wheels with metal pins.
From the physics as well as reducing friction the metal axles allowed the two wheels to be attached at a precise distance on bogies rather than arbitrarily at the ends of a 6 axle, which may be placed a little too far apart causing friction.
Good start to the day to have something train-related as the random part of the day :)
@ambr:
The current design uses wheels with 1L Technic pins, which also creates a fixed distance, but it’s not quite as important as you’d think. One of the resident train-heads in my LUG explained it to me. He said the part of the wheel that actually rides on top of the rail is called a “tire” (yeah, seems weird to refer to it that way). It’s beveled, because rails stay the same distance apart whether the track is curved or straight. On a curve, the inside wheel can press right up to the flange because it only contacts the rail right below the axle. On the outside rail, the flange contacts the rail in front of and behind the axle, forcing the wheel to shift away from that rail. There’s room to spare when it gets on a straight section, so the beveled tires center the train between the two rails, and prevent the flanges from constantly rubbing against the inside surfaces.
The 9v motors, however, need the flanges to stay in constant contact with the rails because the tires are actually plastic with really stiff rubber bands for traction. This is accomplished by spring-loading the flanges so they spread out on the straight section and press into the rails, while on a curve they can compress inward as the contact points shift around on the outer flange.
RC/PF/PU train motor wheels are solid plastic, aside from the traction bands, so they can function more like real driver wheels, and there’s no springs involved. There is a sleeve that drives the axle, and ideally that should stick out just a tiny bit in either side of the motor so you can firmly pinch the wheels against it without causing the inner surface of the wheels to rub against the motor case.
@PurpleDave I have a PhD in engineering yet I feel that my ability to explain the merits/demerits of metal-bar wheel-sets is inferior to yours. Kudos!